1. Field of the Invention
The application relates to a method utilized in a wireless communication and a communication device thereof, and more particularly, to a method of handling system information reception in a wireless communication system and a related communication device.
2. Description of the Prior Art
Long Term Evolution wireless communication system (LTE system), an advanced high-speed wireless communication system established upon the 3G mobile telecommunication system, supports only packet-switched transmission, and tends to implement both Medium Access Control (MAC) layer and Radio Link Control (RLC) layer in one single communication site, so that the system structure becomes simple.
In the LTE system, a user equipment (UE) applies a system information acquisition procedure to acquire system information broadcasted by an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) upon selecting and upon re-selecting a cell, after handover completion, after entering the E-UTRAN from another radio access technology (RAT), upon receiving an indication about the presence of an Earthquake and Tsunami Warning System (ETWS) notification, etc. The system information includes most essential and most frequently transmitted parameters that are needed to acquire other information of a cell for connection establishment.
Toward advanced high-speed wireless communication system, such as transmitting data in a higher peak data rate, LTE-Advanced is standardized by the 3rd Generation Partnership Project (3GPP) as an enhancement of LTE system. LTE-Advanced targets faster switching between power states, improves performance at the cell edge, and includes subjects, such as bandwidth extension, coordinated multipoint transmission/reception (COMP), uplink multiple input multiple output (MIMO), etc.
For bandwidth extension, carrier aggregation is introduced to the LTE-Advanced for extension to wider bandwidth, where two or more component carriers are aggregated, for supporting wider transmission bandwidths (for example up to 100 MHz) and for spectrum aggregation. According to carrier aggregation capability, multiple component carriers are aggregated into overall wider bandwidth, where the UE can establish multiple links corresponding to the multiple component carriers for simultaneously receiving and/or transmitting.
In addition, COMP is considered for LTE-Advanced as a tool to improve coverage of high data rates, cell edge throughput, and system efficiency, which implies dynamic coordination among multiple geographically separated points. That is, when an UE is in a cell-edge region, the UE is able to receive signal from multiple cells, and the multiple cells can receive transmission of the UE.
However, in the LTE system, the system information acquisition is defined for the UE having only one connection to a single cell with a single component carrier. For the UE operated in the LTE-A system, there is no system information acquisition mechanism defined for the UE to acquire system information of additional cells for establishing at least a connection to the additional cells. Therefore, the UE has difficulty in establishing new connections with new cells since the LTE-Advanced system does not specify how the system information acquisition is applied for the UE capable of multiple connections to multiple cells with the same component carrier or different component carriers. Moreover, usage of the system information of the multiple cells is never concerned. Improper usage of the system information of the multiple cells may cause cell configuration problems.
The applicant noticed a mobility management problem related to a tracking area update as below based on a direct image on a basis of a combination of the prior art LTE and LTE-Advanced system. Within an evolved packet core (EPC), a registration area is defined as a set of tracking areas and each of these tracking areas consists of one or more cells that cover a geographical area. Each tracking area is broadcast in a cell, identified by a tracking area code (TAC) and a public land mobile network (PLMN) identifier. The UE considers itself registered to a list of tracking areas and does not need to trigger tracking area update as long as it stays in one of the tracking areas of the list of tracking areas received from the EPC.
Consider a scenario that a UE in a RRC (Radio Resource Control) connected mode has a connection to a cell in a tracking area controlled by a first evolved packet core (EPC1), and is then configured a new connection to a new cell. If the new cell is in a tracing area different from the one that the UE currently registers, the UE performs the tracking area update. Further, if the tracking area of the new cell is controlled by a second EPC (EPC2), the UE notifies the EPC2 of the new tracking area via the tracking area update. Under this situation, the UE becomes a work load of the EPC 2. As can be seen from the above, the UE autonomously performing such tracking area update causes a load change from the EPC1 to EPC2, and the load change is unexpected by the network. Thus, the abovementioned tracking area update is not well controlled by the network, thereby impacting load balance between EPCs.